Apparatus for decorating pressed tins

ABSTRACT

Apparatus for decorating pressed tins by printing a distorted image on a blank which is to be pressed, the apparatus comprising an anamorphic device and a photographic apparatus in which the anamorphic device comprises a truncated cone of transparent material having a perforation along an internal wall in the form a cylinder, the cross section of which is geometrically similar to the cross section of the tin which is to be formed, and the external wall of which is in the form of a truncated cone, the two bases of which are similar to the section of the internal cylinder and a correcting lens the contour of the correcting lens is geometrically similar to the cross section of the finished tin and provides distortions which are determined graphically from an experimental tin.

Inventor Appl. No.

Filed Patented Assignee Priority Lucien Jean Meylan, France 839,384

July 7, 1969 Dec. 14, 1971 Cebal GP Paris, France July 12, 1968 France Y 158928 APPARATUS FOR DECORATING PRESSED TINS 3 Claims, 10 Drawing Figs.

[56] References Cited UNlTED STATES PATENTS 3,073,210 i/l963 Packard 355/47 x 3,238,909 3/1966 Kendall 355 47 x 3,314,329 4/1967 Wolbert 355/52 x Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard A. Wintercorn AnorneyMcDougali, Hersh, Scott & Ladd ABSTRACT: Apparatus for decorating pressed tins by printing a distorted image on a blank which is to be pressed, the apparatus comprising an anamorphic device and a photographic apparatus in which the anamorphic device comprises a truncated cone of transparent material having a perforation along an internal wall in the form a cylinder, the cross section of which is geometrically similar to the cross section of the tin which is to be formed. and the external wall of which is in the form of a truncated cone, the two bases of which are similar to the section of the internal cylinder and a correcting lens the contour of the correcting lens is geometrically similar to the cross section of the finished tin and provides distortions which are determined graphically from an experimental tin.

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APPARATUS FOR DECORATING PRESSED TINS The present invention has as its object an apparatus for decorating pressed tins.

The invention applies to any pressed tins the cross section of which is a closed curve inside which there is at least one point such that any polar half-ray from this point meets the curve at only one point. It applies more particularly to cylindrical tins, the word cylindrical being taken in its most general geometrical sense.

Pressed tins such as tins for preserved food or for drink but also tins containing paint or more generally products intended for sale to the general public are generally decorated by printing either on a sheet of paper or plastics material which is wrapped round the sidewall of the cylinder or on the tin which has already been pressed.

The first process is expensive and not very elegant; the decorative sheet often tears 'either partly or completely, which looks untidy and makes a bad impression. The second process is long and expensive and the possible motifs which can be used for printing in this way are limited.

It is also known from U.S. Pat. No. 3,238,909 to print on a blank", that is to say on a sheet which when pressed constitutes the finished tin, a distorted image of the subject which is to appear on the tin, the preliminary distortion of the subject being produced by anamorphosis so that after the blank has been shaped the desired subject appears on the sidewall of the tin. The anamorphosis is obtained by means of an apparatus comprising, first, an anamorphic device including a luminous and translucent cylinder the cross section of which is geometrically similar to that of the finished pressed tin and which carries a transparent reproduction of the subject to be printed, and a truncated cone-shaped reflector which is mounted coaxially with the aforesaid cylinder and, second, a photographic apparatus for obtaining the distorted image.

This device has the disadvantage of requiring a transparent reproduction of the subject to be printed and it is difficult to produce with precision and preserve over any length of time since it requires a mirror which is perfect as regards its surface definition and the purityof the reflective metal deposit. If any deformation occurs, no repair is possible.

Moreover, this device gives rises to a distorted image, on the one hand owing to the nonlinearity of the elongation of the metal which occurs in pressing, the layers of metal situated at different levels on the sidewall of the resulting tin not undergoing the same amount of deformation, and on the other hand because owing to the anisotropic character of the metal, the tin after pressing has at least four cusps situated in predetermined directions in relation to the direction of rolling of the sheet from which the blank has been cut out, these cusps in practice being frequently four in number situated in directions which form an angle of 50 with the direction of rolling of the sheet. These cusps obviously are cut during the final phase of production of the tin but the decoration on the side of the tin undergoes a corresponding distortion which remains.

The object of the invention is an apparatus for decorating pressed tins by printing on a blank which is to be pressed a distorted image which produces after pressing the subject which is to be printed on the tin, which will be inexpensive, durable and easy to touch up if spoiled and which avoids the distortion which is produced in the decoration of the sidewall of the tin as a result both of the nonlinearity of the distortion of the metal and of the anisotropic character of the metal.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawings in which:

FIG. 1 is a schematic view, partially in section, of an arrangement of elements making up the apparatus of this invention;

FIG. 2 is a developmental view of the sidewalls of a tin to be decorated, which has been photographed to constitute the original;

FIG. 3 shown the distorted image provided by the apparatus, as reproduced on the blank to be pressed;

FIG. 4 shows the tin obtained upon pressing;

FIG. 5 is a view showing the baseline of a rectangular sardine tin with some of the generatrices indicated by reference numerals;

FIG. 6 is a graph for determining the correcting lens;

FIG. 7 is a geometric drawing illustrating the calculation for the correcting lens;

FIG. 8 and 9 are sectional views of the correcting lens along two generatrices referred to by numerals in FIG. 5; and

FIG. 10 is a view of the appearance of curves at the level of the correcting lens of the tin shown in FIG. 5.

The apparatus according to the invention comprises an anamorphic device and a photographic apparatus. It is characterized in that the anamorphic'device comprises, in combination, first, a truncated cone of very transparent optical material which is perforated along an internal wall in the form of a cylinder, the cross section of which is geometrically similar to the cross section of the tin which is to be formed, and the external wall of which is in the form of a truncated cone the two bases of which are similar to the section of the internal cylinder, and, second, a correcting lens the contour of which is geometrically similar to the cross section of the finished tin and which provides distortions which are determined. graphically from an experimental tin.

The apparatus shown in FIG. 1 comprises an anamorphic device comprising a truncated cone 2 and a correcting lens 4, both made of very transparent optical material, and a photographic apparatus 3.

The truncated cone 2 is formed with a central passage defined by an internal wall 22 to form a cylinder the cross section of which is geometrically similar to the cross section of the can to be produced. This cross section is represented as being circular but it may be in the form of any closed curve which has a point preferably situated in its central region, which point will hereinafter be referred to as center", such that any polar half-ray from this point meets the curve at only one point, such as a square, a rectangle, a triangle, an ellipse or any combination of these figures. The external wall 21 of the block 2 is in the form of a truncated cone the two bases of which are similar to the section of the internal cylinder. The two walls 21 and 22 lie on the same axis 300.

The correcting lens 4 has a zone 41 in the region of its axis 300 which consists of a strip with parallel surfaces corresponding to the base of the tin, and around this central zone is a peripheral zone 42 the determination of which is described hereinafter. I

The original 100, that is to say the sidewall of the tin to be formed, which is reproduced photographically, is applied against the internal wall 22 of the truncated cone 2 and then photographed through the correcting lens 4 by the photographic apparatus 3. A negative is obtained which can now be used, if necessary, together with an undistorted negative 120, to represent the decoration of the base of the tin by any known process such as photogravure, offset printing, zerography or any other. The position of the original in the truncated cone, the enlargement of the photographic apparatus and the distance of the correcting lens are obviously so arranged that a negative 110 of the required dimensions is obtained.

When the blank has been pressed, a tin which has the desired subject represented on the sidewall is obtained.

FIG. 1 shows a circular blank for a tin of circular cross section.

The stages of the process are shown in FIGS. 2 to 4.

FIG. 2 represents the original 100, that is to say the sidewall of the tin to be formed, reproduced photographically. The surface has been checkered so that one can more easily understand how this figure will be distorted. After it has been photographed by the apparatus 3, FIG. 3 is obtained: the horizontal lines 101, 102 and 103 are transformed into concentric curves 111, 112, 113 and the vertical lines 104, 105, 106 become straight lines passing through the center 301, namely 114, and 116. A straight line such as 114 passing through the center 301 cuts the curves 111 and 112 at points the distance of which is obtained by multiplying the height of the tin by the inverse ratio of the elongation produced by pressing. It will be noted that the concentric circles 1 11 to 113 are not equidistant, which is due to the correction of the nonlinearity of the distortion of the metal, and that they are distorted, which is due to the correction of the efiect of the cusps.

The drawing shown in FIG. 3 is then applied to the blank which is then pressed (FIG. 4). The drawing on the sidewall takes on the form shown in FIG. 2, which is assumed to be wrapped round the cylindrical wall of the tin.

The material used for the truncated cone 2 preferably has a high-refractive index. As example, on may mention a polymer based on methyl methacrylate which has a transmission power of 92 percent in the visible spectrum and a refractive index of L493 for the D line of sodium at 20 C.

In view of the perfect light transmission and purity of the material, the truncated cone 2 may be lit up either from the outside or by a source of light placed inside its cylindrical cavity.

The distribution of light energy between the reflected rays and the emergent refracted rays depends on the polarization of the light but there is always one ray which is reflected by the truncated cone surface 21 and emerges from the base of the block.

Furthermore, since the exposure times are very short, in fact less than 30 seconds, there is no difficulty in taking into account a reduction in the light energy of the emergent reflected ray when the incident angle of the rays decreases since all that is necessary is to increase the exposure time accordingly.

The total transmission factor can also be considerably improved by improving the transmission of light at the entrance of the image in the truncated cone by immersion, that is to say interposing a liquid between the original 100 and the internal surface 22 of the truncated cone so as to ensure total contact.

Since the object lens 31 is at some distance from the truncated cone 2 the reflected light'ray may be considered to constitute a parallel beam of light, and under these conditions there is no alteration of the image.

An object lens of long focal distance is used with a small aperture.

The use of the truncated cone 2 has the following advantages: the possibility of using either a transparent or an opaque original 100 glued to the' cylindrical wall 22. Only the exposure time, which results from integration of the quantity of reflected light, is different and translates the change of origin of the light and the difference of the path of the light rays into the truncated cone; however, if a transparent original is used the source of light must be situated inside the original whereas if an opaque original is used the source must be placed outside; in either case, a diffuser must be used to prevent the shadows which a direct light could produce; in the case of a transparent original, it can be useful to cover the outside surface 21 of the truncated cone 2 with a thin metallic layer.

Simplification in the execution of the truncated coneshaped anamorphic device, the machining and polishing of the truncated cone made of the plastics material used being very easy; if necessary, retouching may be carried out or damaged surfaces may be repolished without having to fashion a new truncated cone.

The correcting lens is set up as explained below.

An experimental tin is first produced by pressing from a blank contour of which is homothetic with the stated curve: baseline which defines the base of the tin and which is checkered in millimeters, on the generatrices perpendicular to this baseling. By means of this tin one can trace the curves of elongation of the metal as a function of the abscissa x of the point on the blank; FIG. shows the generatrices 117 and 118 in the case of a rectangular tin such as a sardine tin, and in FIG. 6 the lower right-hand curve is the theoretical curve of zero elongation and the upper curve represents the observed elongation, the difference between the ordinates of these two curves being indicated by H which in fact indicates the correction to be made.

If in the anamorphic device described the correcting lens 4 is removed and a prism of small angle A and refractive index n is placed on the optical ray which joins a given point of the image provided by the truncated cone 2 to the object lens and at a distance L from this image, this ray will be deviated by an angle.

The correcting lens constitutes a continuous collection of such prisms, the angle A representing the local inclination of the surface of the lens.

To correct the error AH, one has to make the following calculation (FIG. 7): L=(AH/L)=A(n1) whence:

It is difficult to construct the lens from the inclination of the tangent at each point and moreover it is preferred to define each of these points by its coordinates, the abscissa x and the ordinate y as a function of x operating by graphic integration.

The relationship are as follows:

whence FIG. 8 shows the appearance of the section of the correcting lens along the generatrix 117, and FIG. 9 shows the same section for the generatrix 118. It will be noted that for a sardine tin of the unusual type the differences in thickness in relation to a strip with parallel surfaces are 0.4 mm. for a height of 20 mm. for the generatrix I17 and 1 mm. for the same height for the generatrix I18 situated at a cusp.

Lastly, FIG. 10 shows the curves at the level of the correcting lens for the same tin.

It is to be understood that the correcting lens described may be made in the form of two elements which may or may not be joined together, one of which provides the anisotropic correction and the other the correction for the nonlinearity of the elongation.

It will be understood that changes may be made in the details of construction and operation without departing from the spirit of the invention, especially as defined in the following claims.

Iclaim:

1. An apparatus for decorating pressed tine by printing a distorted image on a blank which is to be pressed but avoids the distortion of the decoration on the sidewall of the tin which may result from nonlinearity of the distortion of the metal and from the anisotropic character of the metal comprising an anamorphic device and a photographic apparatus in which the anamorphic device comprises in combination a truncated cone of transparent optical material having a perforation along an internal wall in the form of a cylinder, the cross section of which is geometrically similar to the cross section of the tin which is to be formed, and an external wall which is in the form of a truncated cone, the two bases of which are similar to the section of the internal cylinder and a correcting lens, the contour of which is geometrically similar to the cross section of the tin to be formed and which provides distortions which correspond to the distortions of the tin to be formed.

2. An apparatus for decorating pressed tins by printing a distorted image on a blank which is to be pressed but avoids the distortion of the decoration on the sidewall of the tin which mayresult from.nonlinearity of the distortion of the metal and from the anisotropic character of the metal comprising an anamorphic device and a photographic apparatus in which the anamorphic device comprises in combination a truncated cone of transparent optical material having a perforation along an internal wall in the form of a cylinder, the cross section of which is geometrically similar to the cross section of the tin which is to be formed, and an external wall which is in the form of a truncated cone, the two bases of which are similar to the section of the internal cylinder and a correcting lens having a central zone formed of a strip with parallel surfaces geometrically similar to the shape of the tin to be formed and a peripheral zone obtained by pressing an experimental tin from a blank on which a checkered design is drawn, said tin enabling the curves of elongation of the metal to be traced as a function of the abscissa x of the given point taken on the blank by noting at each point of the sidewall of this tin the difference AH between the theoretical uniform elongation and the real elongation and then calculating the inclination A of the tangent at each point to the surface of the correcting lens according to the formula:

in which L is the distance of the given point on the correcting lens from the corresponding point of the image given by the truncated cone.

3. An apparatus as claimed in claim 2 in which the correcting lens consists of two elements one of which provides the correction for asymmetry and the other the correction for the nonlinearity of the elongation.

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1. An apparatus for decorating pressed tine by printing a distorted image on a blank which is to be pressed but avoids the distortion of the decoration on the sidewall of the tin which may result from nonlinearity of the distortion of the metal and from the anisotropic character of the metal comprising an anamorphic device and a photographic apparatus in which the anamorphic device comprises in combination a truncated cone of transparent optical material having a perforation along an internal wall in the form of a cylinder, the cross section of which is geometrically similar to the cross section of the tin which is to be formed, and an external wall which is in the form of a truncated cone, the two bases of which are similar to the section of the internal cylinder and a correcting lens, the contour of which is geometrically similar to the cross section of the tin to be formed and which provides distortions which correspond to the distortions of the tin to be formed.
 2. An apparatus for decorating pressed tins by printing a distorted image on a blank which is to be pressed but avoids the distortion of the decoration on the sidewall of the tin which may result from nonlinearity of the distortion of the metal and from the anisotropic character of the metal comprising an anamorphic device and a photographic apparatus in which the anamorphic device comprises in combination a truncated cone of transparent optical material having a perforation along an internal wall in the form of a cylinder, the cross section of which is geometrically similar to the cross section of the tin which is to be formed, and an external wall which is in the form of a truncated cone, the two bases of which are similar to the section of the internal cylinder and a correcting lens having a central zone formed of a strip with parallel surfaces geometrically similar to the shape of the tin to be formed and a peripheral zone obtained by pressing an experimental tin from a blank on which a checkered design is drawn, said tin enabling the curves of elongation of the metal to be traced as a function of the abscissa x of the given point taken on the blank by noting at each point of the sidewall of this tin the difference Delta H between the theoretical uniform elongation and the real elongation and then calculating the inclination A of the tangent at each point to the surface of the correcting lens according to the formula: A (1/n-1) ( Delta H/L) in which L is the distance of the given point on the correcting lens from the corresponding point of the image given by the truncated cone.
 3. An apparatus as claimed in claim 2 in which the correcting lens consists of two elements one of which provides the correction for asymmetry and the other the correction for the nonlinearity of the elongation. 